The present invention relates generally to radio receiver circuitry, and, more particularly, to a system, and associated method therefor, for measuring a signal level of a signal received by a receiver.
In a cellular, communication system, numerous fixed-site transceivers, referred to as "base stations" are installed at spaced-apart locations throughout a geographical area. Each of the base stations contains circuitry to receive modulated signals transmitted thereto, and to transmit modulated signals therefrom. A radio telephone transmits the modulated signals to a base station, and a base station transmits the modulated signals to the radio telephone. Two-way communication is thereby effectuated between a base station and a radio telephone.
A plurality of radio telephones may communicate simultaneously with a single base station when the modulated signals generated by each of the different radio telephones are of dissimilar frequencies. (The signals transmitted by a base station to each of the plurality of radio telephones are also of dissimilar frequencies).
Because a cellular, communication system is formed of a plurality of base stations positioned at spaced-apart locations, continuous communication between a radio telephone and at least one of the base stations defining the cellular, communication system is permitted as long as at least one base station is within the transmission range of the radio telephone. As a radio telephone, such as a mobile phone, may be moved during operation thereof, the radio telephone may first be positioned such that a first base station is within the transmission range of the radio telephone, and then moved such that a second base station is within the transmission range thereof. Responsive to such movement, the base station to which the radio telephone transmits the modulated signal, and the base station from which the radio telephone receives a modulated signal, changes. The process by which this change occurs is referred to as a process of "handing-off". This process of handing-off occurs automatically, without any action taken on the part of a user of the radio telephone.
To determine when a "hand-off" occurs, measurement of the signal levels of signals transmitted by a base station is taken. Responsive to such measurements, the radio telephone transmits information indicative of the signal levels of the signals transmitted thereto, and a base station determines when the "hand-off" should occur. Therefore, accurate measurement of the signal levels of signals received by a radio telephone is essential to ensure optimal operation of a cellular, communication system.
With the increasing popularity of cellular communications, existing cellular, communication systems are, at times, approaching full capacity. Viz., at some times, additional users of a cellular, communication system can not obtain access to the system to communicate thereupon until other users first discontinue communications thereupon. Such occasions most frequently occur during morning and evening rush periods during which the greatest number of users typically desire to make use of the cellular, communication system.
As the range of frequencies permitted of cellular communications is limited, schemes have been developed to utilize more efficiently the available frequencies upon which cellular communication is permitted. For instance, a time division multiplexing technique (and, more particularly, a time division multiple access or TDMA technique) has been adopted in the United States as one means by which the capacity of a cellular, communication system may be increased.
In such a multiplexing technique, a single frequency channel (upon which only one radio telephone transmits or receives a modulated signal in a conventional system) may be shared by more than one radio telephone to permit concurrent use of the same frequency channel. In such a technique, two or more radio telephones transmit sequentially, and in short bursts, modulated signals upon the single frequency channel. Preliminary systems have, in fact, been developed in which a single frequency channel may be shared by three radio telephones to transmit signals concurrently thereupon. In such preliminary systems, a time period is divided into three portions wherein a single radio telephone transmits in one of the three portions, receives information in a second of the three portions, and, during a third of the three portions, the radio telephone may perform other functions. If the signal levels of the signals transmitted thereto by the various base stations could be measured during this third portion of the time period, optimal decisions as to when a "hand-off" should occur between base stations could be made.
However, as each time period is quite short in duration (on the order of thirteen milliseconds in duration), the portion of the time period during which the radio telephone has available to measure the signal levels of the signals transmitted thereto is even more limited.
As determination of the signal levels of signals generated by base stations on data channels requires tuning of the radio telephone to another frequency to such data channels and returning to the first frequency channel to receive a signal during a subsequent time period, only a fraction of the portion of a time period is available to measure the signal levels of signals transmitted to the radio telephone.
The dynamic range of circuitry of the radio telephone is typically limited due to the construction of the circuitry (namely, the circuitry is typically disposed upon integrated circuits, and integrated circuits inherently are of limited dynamic ranges). Therefore, the dynamic range of the circuitry must be adjusted to properly measure the signal levels of signals received by the radio telephone. Such adjustment additionally requires time.
Because of the small amount of time permitted to make a determination of the signal level of the signals transmitted to the radio telephone, existing methods of determining the signal levels of the signals transmitted to the radio telephone are inadequate.
What is needed, therefore, is an improved system for measuring a signal level of a signal received by a receiver.